The inventions (variants) are intended for improvement of calibration precision of digital X-ray apparatuses: computed tomographs, as well as digital X-ray apparatuses equipped with C-arm and U-arm type stands, which method is based on calculation of mechanical instability of the stand. Calibration method for X-ray apparatus, in which one or two X-ray contrast balls of different diameters are placed in the scanning field, excluding its centre, a series of images of the scanning field with different angles of the stand rotation are obtained, the X-direction and Y-direction regular components of mechanical instability of the X-ray apparatus stand are determined using the coordinates of projection centre of the ball, X-direction and Y-direction calibration modifications set for mechanical instability of the stand are formed, which modifications are used for correction of the images, according to the invention the additional regular component of mechanical instability of digital X-ray stand is determined using the scales of projections, and the calibration data set for mechanical instability of the stand, which includes the scale calibration modifications, is formed.